Helical face gears for use in differentials are known in the art, as set forth for example, in U.S. Pat. Nos. 3,253,483 and 4,791,832. However, the incorporation of helical face gears into differentials has not been commonly utilized because of, for example, challenges with respect to the strength of the gears, the expense in manufacturing gear components with acceptable tolerances, and the difficulty in ensuring equal torque sharing among the gear components.
In a differential including a helical face gear, a helical pinion, and a pinion housing, the differential may be configured to split torque among multiple helical pinions that may be disposed within the pinion housing. The pinion housing may comprise a generally annular ring having at least one aperture extending radially inwardly from an outer radial surface of the pinion housing. Each aperture may comprise a blind aperture that is closed by a wall defining an inner radial surface of the pinion housing. A helical pinion may be disposed in each blind aperture. Each helical pinion may include a protrusion at one end of the helical pinion that is designed for the purpose of piloting or guiding the pinion within the pinion housing. The protrusion may extend in the direction along the longitudinal axis of the helical pinion. The protrusion may be smaller in diameter than the diameter of the helical pinion. The small diameter of the protrusion may result in relatively poor piloting of the helical pinion. The end of the helical pinion that includes the protrusion may be in contact with the wall of the pinion housing that defines an inner radial surface of the pinion housing. Due to friction between the contacting surfaces of the end of the helical pinion and the pinion housing, heat may be generated. The heat exchange between the components of the differential may be poor due to the thin wall of the pinion housing at the area of contact with the helical pinion. In addition, the gear components may encounter errors caused by the manufacturing of gear components, the assembly of the differential, and/or the deformation of gear components under an operating load, all of which may be unavoidable and may cause unequal torque sharing among the pinions of a differential. When there is unequal torque sharing among the pinions of a differential, this may result in low torque capacity. In addition, the use of a blind aperture may result in more difficult manufacturing of the pinion housing. Because the longitudinal axis of the blind aperture may need to be aligned with the longitudinal axis of the helical pinion itself as well as the longitudinal axis of the protrusion on the helical pinion, the tolerances for the pinion housing and the helical pinion is very tight, further complicating manufacturing of the differential.
It may be advantageous to improve piloting of the helical pinion in the pinion housing and to optimize torque sharing among multiple helical pinions that may be disposed in the pinion housing, both of which may result in significantly higher torque capacity of the differential. It may also be advantageous to improve the conditions of heat exchange in the areas of the differential where friction is generated because of the contacting surfaces of the helical pinion and the pinion housing. In addition, it may be advantageous to improve the manufacturability of the differential without requiring costly changes in manufacturing methods to increase accuracy for manufacturing of helical pinions and the pinion housing that may not be commercially viable in the high volume production of differential with gear sets with split torque.